This invention relates to a monomer for synthesizing a self-doped conductive polymer, a process of producing the monomer, a self-doped conductive polymer, and a process of producing a self-doped conductive polymer.
The terminology xe2x80x9cself-doped conductive polymerxe2x80x9d means a polymer having a functional group serving as a dopant covalently bonded to the backbone thereof either directly or via a spacer so as to have controlled conductivity.
While the present invention will be described with particular reference to poly[(2,5-dipropoxysulfonic acid)phenylene-1,4-vinylene] as a self-doped conductive polymer (hereinafter referred to as a self-doped PPV), the present invention is not limited thereto. The present invention is applicable to synthesis of any aromatic monomer from a benzene or naphthalene derivative having a hydroxyl group bonded to its aromatic nucleus and self-doped conductive polymers obtained therefrom.
Conductive polymers have been engaging attention for applications in the electric and electronic industries as various conductive materials or optical materials providing parts demanding high processability, such as electrodes, sensors, electronic display devices, nonlinear optical devices, and photoelectric devices, antistatic agents, automotive parts, electromagnetic shields, and the like.
Poly(phenylene vinylene)s (PPVs) have recently been of interest as conductive polymers partly because of their ease of handling. PPVs can be rendered self-doped by introducing a self-doping group thereby to enjoy improvements in conductivity, safety, and the like.
Introduction of an alkoxysulfonic acid group, one of self-doping groups, into an aromatic ring of a conductive polymer has been carried out by, for example, a process starting with an aromatic compound having a halogen directly bonded to the aromatic ring there as illustrated below. 
wherein n is an integer; and X is Cl or Br.
That is, a self-doping group-containing compound (III) is synthesized by once substituting the halogen atom of a compound (I) with an alkoxy group, to which a sulfonic acid group is added. The resulting compound (III) is chloromethylated to obtain a monomer (IV) having a self-doping group and a polymerizable group (chloromethyl group) which is ready to be polymerized to produce a self-doped conductive polymer.
Each step involved in the above-mentioned conventional process of producing a self-doping monomer involves difficulty in purifying the product, which has resulted in poor overall yield. In addition, the self-doping group of the monomer is apt to cause a side reaction in the polymerization reaction, tending to result in a failure to obtain a desired self-doped conductive polymer.
An object of the present invention is to provide a process for producing a self-doped conductive polymer in high yield without involving a side reaction during polymerization.
As a result of intensive investigations, the present inventors have reached the present invention.
The invention provides, in its first aspect, a process of producing a monomer for synthesizing a self-doped conductive polymer characterized by starting with a benzene or naphthalene derivative (e.g., hydroquinones and phenols) having a hydroxyl group. That is, the invention provides a process of producing a monomer for synthesizing a self-doped conductive polymer comprising introducing an alkoxysulfonic acid group as a self-doping group to a benzene or naphthalene derivative having a hydroxyl group bonded to the aromatic ring thereof by alkanesulfonation of the hydroxyl group, protecting the self-doping group by converting to an acid halide form by sulfonyl halogenation, and introducing a chloromethyl group as a polymerizable group into the aromatic ring.
It is preferred for the starting benzene or naphthalene derivative to have two hydroxyl groups for providing conductive polymers having two self-doping groups per repeating unit, which favors reaching a desired conductivity.
It is preferred for the alkanesulfonic acid used for the alkanesulfonation has a straight-chain alkane moiety containing 2 to 12 carbon atoms. With only one carbon atom in the alkane moiety, the electron attraction by the sulfonic acid moiety reduces the electron density on the conductive polymer, resulting in a reduction of conductivity. Too many carbon atoms in the alkane moiety makes the side chain too bulky to allow polymer main chains to come into contact with each other or get close to each other. As a result, electron conduction would be hindered to reduce the conductivity.
Thionyl chloride is a preferred chlorinating agent for achieving the sulfonyl halogenation with no side reactions. Other halogenating agents are useful as well unless they cause a side reaction or influence the subsequent reaction.
The invention provides, in its second aspect, a monomer for synthesizing a self-doped conductive polymer prepared by the above-described process which is represented by formula (1): 
wherein m represents 1 or 2; n represents an integer of 2 to 12; and X represents chlorine or bromine.
The invention also provides, in its third aspect, a process of producing a self-doped conductive polymer by using an aromatic monomer prepared by the above-described process.
That is, the invention provides a process of producing a self-doped conductive polymer which comprises converting the chloromethyl group of the aromatic monomer into a sulfonium salt form, polycondensing the sulfonium salt monomer to form an intermediate polymer, releasing the sulfonium salt moiety from the intermediate polymer to form a phenylene vinylene backbone or a naphthylene vinylene backbone, and deprotecting the protected self-doping group by oxidation.
The invention also provides a process of producing a self-doped conductive polymer which comprises dehydrohalogenation polymerization of the aromatic monomer at the polymerizable group to form a phenylene vinylene backbone or a naphthylene vinylene backbone and deprotecting the protected self-doping group by oxidation.
The invention also provides, in its fourth aspect, a self-doped conductive polymer represented by formula (2): 
wherein 1 represents an integer of 10 to 104; m represents 1 or 2; and n represents an integer of 2 to 12, which is synthesized by the above-described processes.
Having a phenylene vinylene backbone and a naphthylene vinylene backbone, the self-doped conductive polymer represented by formula (2) has a pi-electron conjugated structure and exhibits relatively satisfactory conductivity, high processability, and ease of handling.